638

Novel carbazole–pyridine copolymers by aneconomical method: synthesis, spectroscopic and

thermochemical studiesAamer Saeed*1, Madiha Irfan1 and Shahid Ameen Samra1,2

Full Research Paper Open Access

Address:1Department of Chemistry, Quaid-i-Azam University, Islamabad,Pakistan and 2Kohat University of Science and Technology (KUST),Kohat, 26000, NWFP, Pakistan

Email:Aamer Saeed* - aamersaeed@yahoo.com

* Corresponding author

Keywords:carbazole–pyridine copolymers; fluorescent materials; organic lightemitting diode (OLED); photoluminescence spectra; UV spectra

Beilstein J. Org. Chem. 2011, 7, 638–647.doi:10.3762/bjoc.7.75

Received: 02 November 2010Accepted: 12 April 2011Published: 19 May 2011

Associate Editor: H. Ritter

© 2011 Saeed et al; licensee Beilstein-Institut.License and terms: see end of document.

AbstractThe synthesis, as well as spectroscopic and thermochemical studies of a novel class of carbazole-4-phenylpyridine co-polymers are

described. The synthesis was carried out by a simple and cheaper method compared to the lengthy methods usually adopted for the

preparation of carbazole–pyridine copolymers which involve costly catalysts. Thus, two series of polymers were synthesized by a

modified Chichibabin reaction, i.e., by the condensation of diacetylated N-alkylcarbazoles with 3-substituted benzaldehydes in the

presence of ammonium acetate in refluxing acetic acid. All the polymers were characterized by FTIR, 1H NMR, 13C NMR, UV–vis

spectroscopy, fluorimetry, TGA and DSC. The weight average molecular masses (Mw) of the polymers were estimated by the laser

light scattering (LLS) technique.

638

IntroductionAn immense research effort has been focused on organic semi-

conductors, including polymers, oligomers, dendrimers, small

molecules and heavy-metal complexes, after the discovery by

Burroughes et al. in 1990 [1-6] that they can be used for fabri-

cating organic light emitting diodes (OLEDs). A number of

criteria exist for employing organic materials as LEDs [7] and

carbazole containing polymers are the most studied group

amongst the different polymers intended for OLED applica-

tions [8-15]. Carbazole containing polymers exhibit excellent

electron-donating properties together with intense lumines-

cence, high thermal stability and excellent photoconductivity.

Furthermore, the functionalization of the carbazole nucleus can

easily be carried out at the 3-, 6- and 9-positions to afford a

great diversity of structures [16]. Carbazole containing poly-

mers have been greatly explored during the last few years for

their applications in organic electronic devices [8]. New conju-

gated, fully aromatic poly-2,7-carbazole derivatives have been

synthesized that exhibit high glass transition temperatures, high

Beilstein J. Org. Chem. 2011, 7, 638–647.

639

Scheme 2: Synthesis of poly[3,6-N-alkylcarbazole-4-(3-substituted phenyl)pyridine-2,5-diyl]. i) CH3COONH4, CH3COOH, reflux, 18 h.

molecular weights and stability, and that have excellent power

efficiency with low bandgaps [17,18]. Alternating poly-2,7-

carbazole polymers show good thermoelectric properties [19].

Carbazole–pyridine alternate copolymers are a fascinating class

of polymers on account of the fact that they take advantage of

the combination of the electron-donating properties of carbazole

and electron-withdrawing properties of the pyridine ring [20].

Zheng et al. have prepared a new class of copolymers that

incorporate pyridine and N-alkyl carbazole alternatively into the

main chain by oxidative-coupling copolymerization. These

polymers are thermostable, highly soluble, and processable, and

the fluorescence spectra of the polymers display blue light emit-

ting properties [21].

In view of the above literature reports, it was thought to be of

considerable interest to synthesize carbazole–pyridine copoly-

mers by a route that involved the synthesis of the pyridine units

as a polymer analogous reaction. To the best of our knowledge,

there is no previous report of such a synthesis; the nearest

precedent is the use of a Friedländer synthesis to prepare

polyquinolines by Jenekhe [22]. Herein, we report a cost-effec-

tive synthesis of carbazole–pyridine copolymers in contrast to

the protracted and costly methods which involve expensive

catalysts.

Results and DiscussionThe synthetic pathway employed to prepare the monomers is

outlined in Scheme 1. N-Butyl and N-octylcarbazoles were

synthesized by heating a mixture of carbazole and the respec-

tive alkyl halide in a two phase system of aqueous KOH (50%)

and benzene in the presence of tetrabutylammonium bromide

(TBAB) as a phase-transfer catalyst [23-25]. The N-alkylcar-

bazoles were subsequently subjected to Friedel–Crafts acetyla-

Scheme 1: Synthesis of the monomers. i) R–Br, 50% KOH, benzene,TBAB, 80 °C, 2 h; ii) AcCl, AlCl3, CHCl3, 0 °C then rt, 3 h.

tion at the active positions of carbazole, viz. 3 and 6, with anhy-

drous aluminum chloride in dry chloroform [26].

The monomers were purified by recrystallization. The diacetyl-

ated carbazole monomers were heated under reflux with various

3-substituted benzaldehydes and ammonium acetate in glacial

acetic acid in a modified Chichibabin reaction to assemble the

pyridine ring in situ and afford the desired polymers (Scheme 2)

[27].

The construction of the pyridine ring in situ by reaction of di-

acetylated carbazole monomers with different benzaldehydes

and ammonium acetate may be envisaged by the complex

sequence shown in Scheme 3 which involves protonation,

enolization, deprotonation, dehydration, the nucleophilic addi-

tion of ammonia, intramolecular cyclization and aromatization.

The polymers were obtained by pouring the reaction mixture

into distilled water, followed by filtration and washing of the

residue with copious quantities of distilled water to remove

completely acetic acid and salts. Finally, the polymers were

dissolved in THF and re-precipitated thrice in methanol to

Beilstein J. Org. Chem. 2011, 7, 638–647.

640

Scheme 3: Proposed mechanism of pyridine ring formation.

Beilstein J. Org. Chem. 2011, 7, 638–647.

641

remove oligomers. The polymers were obtained as yellow to

brown powders which were then dried in a vacuum oven. The

polymers were readily soluble, at room temperature, in a variety

of common solvents such as tetrahydrofuran, dichloromethane,

chloroform and acetone.

All polymers were characterized on the basis of FTIR, 1H NMR

and 13C NMR spectroscopic analysis. The IR spectral data of all

polymers showed the characteristic peaks of C=N stretching at

1590–1584 cm−1, aromatic tertiary C–N stretching at

1354–1340 cm−1, and C–N stretching at 1153–1143 cm−1

showing the formation of the pyridine ring. The peaks at 3415

and 1523 cm−1 indicating the presence of OH- and NO2- groups

respectively, were also observed in the corresponding polymers.

Figure 1b shows the 1H NMR spectrum of the polymer

P1a whilst that of corresponding monomer is shown in

Figure 1a.

A comparison of the 1H NMR spectra of the monomer to that of

the polymer indicates the disappearance of a peak due to acetyl

protons at δ 2.75 ppm in addition to the appearance of a number

of new peaks in the aromatic region. A complex pattern of split-

ting in the aromatic region and the characteristic peak broad-

ening was also observed consistent with the in situ formation of

the pyridine ring and polymerization. Polymer solutions in THF

were subjected to GPC using polystyrene standards for the

determination of the molecular weights, however, no elution

was observed for any of the polymers. Therefore, molecular

weights could not be determined by GPC, because no standard

column was found to be compatible with this type of polymer.

Consequently, it was decided that the molecular weights would

be determined by the LLS technique, and the results are given

in Table 1.

In the static laser light scattering (LLS) technique, the angular

dependence of the excess absolute time-average scattered inten-

sity, the so-called Raleigh ratio Rvv(q) at a scattering angle θ is

measured. The molecular weights of the polymers in a dilute

solution at a concentration C can then be obtained on the basis

of the following equation:

where K = 4π2n2(dn/dC)2/(NAλ04), q = (4πn/λ0)sin(θ/2) and NA,

dn/dC, n, λ0, and θ being Avogadro's number, the specific

refractive index increment, the solvent refractive index, the

wavelength of the light in vacuo, and the scattering angle, res-

pectively. Mw is the weight average molar mass, A2 is the

second virial coefficient, and <Rg2>z

1/2 is the root-mean square

Z-average radius of gyration of the polymer chain.

Figure 1: 1H NMR spectra of (a) monomer 2a and (b) polymer P1a.

By measuring Rvv(q) at a set of C and θ, Mw, <Rg>z and A2 can

be determined from a conventional Zimm plot which incorpo-

rates q and C extrapolation on a single grid. There are experi-

mental points at all grid points except along the lower line (the

θ = 0 line) and the left-most line (the C = 0) line. The values of

Mw and <Rg>z were calculated from the slopes of [KC/Rvv

(q)]C→0 vs q2 and [KC/Rvv (q)]q→0 vs C and the intercept of

[KC/Rvv (q)]q→0,C→0, respectively. Figure 2 shows the Zimm

plot of P2a in THF at room temperature.

Thermochemical properties of the polymersThe thermal properties of the two series of polymers, P1 and P2

were investigated by thermogravimetric analysis (TGA) and

differential scanning calorimetry (DSC). For TGA the samples

were heated (PerkinElmer Thermal Analysis System 409) from

25 °C to 85 °C at a rate of 10 °C/min and at a nitrogen gas flow

Beilstein J. Org. Chem. 2011, 7, 638–647.

642

Table 1: Thermal data and molecular weights for polymers P1 and P2.

P1a P1b P1c P1d P2a P2b P2c P2d

(Mw) 105 (g/mol)a 0.57 0.56 0.75 0.12 1.28 2.43 1.73 1.29Td (°C)b 380 300 265 300 376 295 400 295Tg (°C)c 154 165 161 170 158 160 158 164

aMolecular weights of polymers of series P1 and P2 by static LLS. bDecomposition temperature Tg determined by TGA at a heating rate of 10 °C/minunder a N2 atmosphere. cGlass transition temperature Tg determined by DSC at a heating rate of 10 °C/min under a N2 atmosphere, 2nd run.

Figure 4: TGA curves of polymers (a) P1 and (b) P2.

Figure 2: Zimm plot for P2a in THF at room temperature.

rate of 80 mL/min. Polymers P1 and P2 lost weight gradually

during the early phase of the experiment. A thermal gravi-

metric analysis curve of P1a is shown in Figure 3.

The thermal analysis results indicated that polymers P1 and P2

have a high decomposition temperature Td and good thermal

stability above 300 °C, which is very attractive for the fabrica-

tion of stable organic electroluminescent devices. TGA thermo-

Figure 3: Thermogravimetric analysis curve of P1a.

grams for polymers P1 and P2 are shown in Figure 4 and the

results of the thermal analysis are shown in Table 1.

For DSC, the samples were first heated to melting, then cooled

to the glassy state and reheated to determine the glass transition

temperature (Tg). A representative DSC graph is shown for P1a

in Figure 5. Tg is calculated from the second heating curve. As

it can be seen from the graph, Tg for the polymer is 154 °C. All

the polymers show glass transition temperatures above 150 °C

(Table 1).

Beilstein J. Org. Chem. 2011, 7, 638–647.

643

Table 2: Absorption and emission spectroscopic data for polymers P1 and P2.

P1a P1b P1c P1d P2a P2b P2c P2d

λabs,max [nm] 301 282 285 300 291 284 291 289λem,max [nm] 417 424 397 (491) 421 426 435 400 (524) 431

Figure 6: UV–vis spectra of the polymers of (a) series P1 and (b) series P2.

Figure 5: DSC graph for polymer P1a.

Photophysical properties of the polymersThe photophysical properties of the polymer, including absorp-

tion and emission spectral studies, were determined from solu-

tions in chloroform. A summary of the measured spectroscopic

data is given in Table 2.

Figure 6 shows the absorption spectra for the two series of poly-

mers. The solution of P1a exhibited an absorption maximum at

301 nm along with a shoulder at a higher wavelength. Similarly,

P1b, P1c and P1d had λmax values of 282, 285 and 300 nm, res-

pectively. Distinct shoulders are observed for all of the four

polymers at higher wavelengths. Similar spectra were obtained

for polymers of P2 series. The λmax values were 291, 284, 291

and 289 nm for P2a, P2b, P2c and P2d, respectively, along

with distinct shoulders. The main peaks on the spectra are

attributed to a π→π* transition, and the shoulders correspond to

n→π* transitions in the respective materials. A comparison of

the photophysical properties of the synthesized polymers may

be made with structurally related polymers previously synthe-

sized by Zheng et al. [21,28]. The observed differences in the

absorption spectra of both polymer series arise due to the differ-

ence in alkyl chain lengths. As the chain length increases, there

is a marked decrease in the bandwidth of the absorption and

emission bands [29]. By comparing both series of polymers, the

absorption maxima shifts to an upper limit with increasing

chain length [30]. Furthermore, polymers with similar groups in

both series show similar absorption maxima, but the apparent

differences from one another are due to the difference in the

electron-donating and electron-withdrawing nature of the

substituents. The additional peak in the absorption spectrum of

P1c is due to the optical transition attributed to the presence of

the auxochromic OH group, which increases the conjugation

length [31] and becomes part of extended chromophore. This

effect is absent in the other compounds.

The photoluminescence spectra of the polymer solutions of

series P1 and P2 in CHCl3 are shown in Figure 7. Polymers

P1a, P1b, P1c and P1d show emission maxima at 417, 424,

397 and 421 nm, respectively, whereas polymers P2a, P2b, P2c

Beilstein J. Org. Chem. 2011, 7, 638–647.

644

Figure 7: Photoluminescence spectra of polymers P1and P2 in CHCl3 solution.

Figure 8: (a) Polymers of P2 series in visible light; (b) observed fluorescence (CHCl3 dilute solutions) under UV irradiation (254 nm).

and P2d show maxima at 426, 435, 400 and 431 nm, respective-

ly. Polymers P1c and P2c having hydroxyl functionality show

an extra emission band at 491 and 524 nm, respectively. These

suggest that the polymer solutions in CHCl3 should emit

blue–green light.

The emission colors of dilute solutions of the polymer samples

were also observed under UV light and are shown in Figure 8.

ConclusionA new class of polymeric materials that contain alternating hole

transporting and electron transporting moieties of carbazole and

pyridine, respectively, has been synthesized by a simple and

inexpensive method. The polymers are highly soluble in most

common solvents, which makes them easily to process by spin

coating methods. These materials can be considered as poten-

tial candidates for application as OLEDs. The synthesis of

further polymers of this novel class is underway.

ExperimentalMelting points were recorded using a digital Gallenkamp

(Sanyo) model MPD BM 3.5 apparatus and are uncorrected.

1H and 13C NMR spectra were determined in deuterochloro-

form solutions using a Bruker AM-300 spectrophotometer.

FTIR spectra were recorded on an FTS 3000 MX spectropho-

tometer. Mass spectra (EI, 70eV) were obtained on a GC–MS

instrument of Agilent technologies. UV–vis and fluorescence

spectra were recorded on a Perkin Elmer Lambda 20

UV–visible spectrophotometer and a Perkin Elmer LS 55 fluo-

rescence spectrophotometer, respectively.

Molecular weights of the polymers were determined by

the laser light scattering (LLS) technique using a commercial

light-scattering spectrometer (ALV/SP-150 equipped with

an ALV-5000 multi-τ digital time correlator) with a

solid-state laser (ADLAS DPY 425II, output power ≈ 400 mW

at λ = 532 nm) as the light source. Thermogravimetric

analysis (TGA) was performed with a PerkinElmer Thermal

analysis System 409. Differential scanning calorimetry (DSC)

measurements were performed using Bruker Reflex II ther-

mosystem. The TGA and DSC measurements were recorded

under a nitrogen atmosphere at a heating rate of 10 °C/min.

Elemental analyses were performed on CHNS 932 LECO

instrument.

Beilstein J. Org. Chem. 2011, 7, 638–647.

645

Carbazole, 1-bromobutane, 1-bromooctane, tetrabutylammo-

nium bromide (TBAB) and aluminum chloride were commer-

cial products from Fluka; acetyl chloride, benzaldehydes and

ammonium acetate were purchased from the Aldrich Chemical

Company. Glacial acetic acid was purchased from Riedel

de-Haën.

Synthesis of 9-butylcarbazole (1a)A mixture of carbazole (8.35 g, 50 mmol), 1-bromobutane

(7.13 g, 52 mmol), benzene (25 mL), 50% KOH aqueous solu-

tion (60 mL), tetrabutylammonium bromide (TBAB, 0.4 g,

1.25 mmol) was stirred at 80 °C for 2 h. The reaction mixture

was cooled to room temperature. The benzene layer was sep-

arated, diluted with 20 mL of ethyl acetate, washed with three

50 mL portions of water and dried over anhydrous MgSO4.

Solvents were removed in vacuo to give a viscous oil, which

solidified on standing at room temperature to afford a white

solid. Recrystallization from ethanol gave 1a as white needles

(92%). Mp 54–56 °C; IR (KBr, υ/cm−1): 1640, 1350, 1153;1H NMR (CDCl3, 300 MHz): δ 8.16 (d, J = 7.8 Hz, 2H), 7.51

(m, 4H), 7.28 (d, J = 7.6 Hz, 2H), 4.35 (t, J = 7.2 Hz, 2H), 1.90

(m, 2H), 1.45 (m, 2H), 0.99 (t, J = 7.2 Hz, 3H); 13C NMR

(CDCl3, 75 MHz): δ 140.7, 125.5, 122.8, 120.3, 118.7, 108.6,

42.8, 31.17, 20.62, 13.95; Elemental analysis: Calcd C: 86.0%,

H: 7.6%, N: 6.2%; found C: 85.8%, H: 7.5%, N: 6.1%.

9-Octylcarbazole (1b)The compound 1b was synthesized by the same procedure as

for 1a using carbazole (8.35 g, 50 mmol), 1-bromooctane

(10.0 g, 52 mmol), benzene (25 mL), and TBAB (0.4 g,

1.25 mmol). The product was obtained as a light-yellow

oil (87%). IR (NaCl cell, υ/cm−1): 1630, 1340, 1147; 1H NMR

(CDCl3, 300 MHz): δ 8.35 (d, J = 7.8 Hz, 2H), 7.69 (m, 4H),

7.59 (d, J = 8.1 Hz, 2H), 4.41 (t, J = 7.2 Hz, 2H), 2.03 (m, 2H),

1.51 (m, 5H), 1.14 (t, J = 7.2 Hz, 3H); 13C NMR (CDCl3,

75 MHz): δ 140.5, 125.8, 123.0, 120.5, 118.9, 108.9, 43.1, 32.1,

29.6, 29.4, 29.2, 27.5, 22.9, 14.4; Elemental analysis: Calcd C:

85.9%, H: 9.0%, N: 5.0%; found C: 85.8%, H: 8.9%, N: 5.0%.

3,6-Diacetyl-9-butylcarbazole (2a)Aluminum chloride, (4.0 g, 3 mmol) and acetyl chloride,

(2.35 g, 3 mmol) were added successively to 10 mL of dry chlo-

roform. The mixture was stirred for 10 min at 0 °C to obtain a

clear solution. A solution of (4.46 g, 2 mmol) of 1a in 10 mL of

dry chloroform was added dropwise to the above solution at

0 °C during 15 min. The reaction mixture was stirred at room

temperature for 3 h. After the completion of the reaction (TLC

monitoring), the reaction mixture was poured into a stirred solu-

tion of 10% HCl (50 mL). The organic layer was separated,

washed with distilled water three times and dried over anhy-

drous Na2SO4. The solvent was removed in vacuo to give a

solid which was recrystallized from ethanol to afford 2a (85%)

as dull green crystals with a moldy bread smell. Mp 145 °C; IR

(KBr, υ/cm−1): 2907, 1718, 1655, 1348, 1145; 1H NMR

(CDCl3, 300 MHz): δ 8.79 (s, 2H), 8.18 (dd, J = 8.7 Hz, 2H),

7.45 (d, J = 8.4 Hz, 2H), 4.35 (t, J = 7.2 Hz, 2H), 2.75 (s, 6H),

1.87 (m, 2H), 1.42 (m, 2H), 0.97 (t, J = 7.2 Hz, 3H); 13C NMR

(CDCl3, 75 MHz): δ 197.4, 143.9, 129.6, 127.0, 122.8, 122.0,

108.9, 43.3, 31.0, 26.6, 20.4, 13.8; GC–MS (m/z): 307 (M.+),

264 (100%), 221, 178, 43, 29.

3,6-Diacetyl-9-octylcarbazole (2b)The compound 1b was synthesized by the same procedure as

for 2a from AlCl3, 4.00 g (3 mmol), acetyl chloride, 2.35 g

(3 mmol) to afford 1b 5.58 g (2 mmol) in 88% yield as dull

green crystals. Mp 139 °C; IR (KBr, υ/cm−1): 2939, 1715, 1640,

1350, 1140; 1H NMR (CDCl3, 300 MHz): δ 8.75 (s, 2H,

Ar-1,1’), 8.18 (dd, 2H, J = 8.4 Hz, Ar-2,2’), 7.45 (d, 2H, J =

8.7 Hz, Ar-3,3’), 4.34 (t, 2H, J = 7.2 Hz, H-a), 2.75 (s, 6H,

COCH3), 1.86 (m, 2H, H-b), 1.30 (m, 10H, H-c,d,e,f,g), 0.86 (t,

3H, J = 6.9 Hz, H-h); 13C NMR (CDCl3, 75 MHz): δ 198.1,

142.4, 128.9, 127.0, 121.8, 120.3, 109.9, 43.1, 31.0, 29.3, 28.9,

27.2, 22.4, 13.8; GC–MS (m/z): 363 (M.+), 264 (100%), 348,

221, 178, 43, 29.

General procedure for the synthesis of polymers P1and P2 (a–d)Ammonium acetate (10 mmol) was added portionwise to a

stirred equimolar mixture of 3,6-diacetyl-N-alkylcarbazole

and benzaldehyde in acetic acid (10 mL). The reaction mixture

was heated under reflux for 18 h. Upon completion of reaction

(TLC monitoring), the reaction mixture was cooled to room

temperature, poured into distilled water (20 mL) and stirred

for 5 min. The precipitated solid was filtered and washed

well with copious quantities of distilled water to remove acetic

acid and salts completely. The resulting solid was dissolved in

THF and precipitated by adding methanol to remove the

oligomers. The precipitation process was repeated three times

and the polymers obtained were dried in a vacuum oven at

70 °C overnight.

Poly{[N-butylcarbazole-3,6-diyl][4-phenylpyridine-2,6-diyl]} (P1a)Yellow solid; yield: 44%; IR (KBr, υ/cm−1): 3055, 2930, 2860,

1658, 1584, 1326, 1153; 1H NMR (CDCl3, 300 MHz): δ 8.94

(s, Ar-1), 8.55 (dd, J = 8.4 Hz, Ar-2), 8.28 (d, J = 8.4 Hz,

Ar-H), 8.0–7.5 (m, Ar H), 4.4 (t, 2H, J = 6.9 Hz, H-a), 1.7 (m,

4H, H-b,c), 1.0 (t, 3H, J = 6.9 Hz, H-d); 13C NMR (CDCl3,

75 MHz): δ 148.6, 146.2, 144.1, 142.3, 139.8, 137.2, 129.0,

128.7, 127.5, 120.5, 119.1, 116.7, 109.5, 33.2, 29.9, 29.2, 28.7,

27.2, 21.9, 14.8; Elemental analysis: Calcd C: 86.6%, H: 5.8%,

N: 7.4%; found C: 84.3%, H: 5.9%, N: 7.1%.

Beilstein J. Org. Chem. 2011, 7, 638–647.

646

Poly{[N-butylcarbazole-3,6-diyl][4-(3-nitrophenyl)-pyridine-2,6-diyl]} (P1b)Yellow powder; yield: 49%; IR (KBr, υ/cm−1): 3035, 2930,

2890, 1656, 1585, 1523, 1345, 1145, 800; 1H NMR (CDCl3,

300 MHz): δ 8.96 (s, Ar-8), 8.58 (s, Ar-7), 8.27 (m, Ar-H), 8.0

(d, J = 7.8 Hz, Ar-5), 7.92 (s, Ar-4), 7.66 (d, J = 8.1 Hz, Ar-3),

7.54 (m, Ar-H), 4.4 (t, 2H, J = 7.1 Hz, H-d), 1.9 (m, 2H, H-c),

1.46 (m, 2H, H-b), 1.0 (t, 3H, J = 7.2 Hz, H-a); 13C NMR

(CDCl3, 75 MHz): δ 148.9, 144.5, 142.0, 137.1, 134.3, 130.5,

130.0, 127.8, 124.9, 124.5, 123.3, 122.1, 108.7, 33.5, 29.3, 27.6,

22.6, 14.8; Elemental analysis: Calcd C: 77.3%, H: 5.0%, N:

10.0%; found C: 76.9%, H: 4.7%, N: 9.8%.

Poly{[N-butylcarbazole-3,6-diyl][4-(3-hydroxy-phenyl)pyridine-2,6-diyl]} (P1c)Dark brown powder; yield: 40%; IR (KBr, υ/cm−1): 3415, 3110,

2955, 2860, 1663, 1584, 1354, 1146; 1H NMR (CDCl3, 300

MHz): δ 8.79 (s, Ar-1), 8.21 (dd, J = 1.9, 9.0 Hz, Ar-2),

7.47–7.41 (m, Ar-H), 7.31–7.18 (m, Ar-H), 7.02–6.99 (m,

Ar-H), 5.10 (s, OH), 4.34 (t, 2H, J = 9.0 Hz, H-a), 1.93–1.79

(m, 2H, H-b), 1.44–1.35 (m, 2H, H-c), 0.97 (t, 3H, J = 9.0 Hz,

H-d); 13C NMR (CDCl3, 75 MHz): δ 150.1, 147.1, 144.3,

141.6, 139.7, 137.8, 134.4, 131.1, 129.3, 126.2, 125.4, 122.9,

120.4, 117.1, 109.3, 36.2, 29.3, 28.5, 28.1, 25.5, 22.2, 14.6;

Elemental analysis: Calcd C: 83.0%, H: 5.6%, N: 7.1%; found

C: 82.6%, H: 5.3%, N: 6.8%.

Poly{[N-butylcarbazole-3,6-diyl][4-(3-bromophenyl)-pyridine-2,6-diyl]} (P1d)Yellow precipitate; yield: 66%; Rf: 0.45; IR (KBr, υ/cm−1):

3065, 2960, 2890, 1652, 1596, 1340, 1143, 664; 1H NMR

(CDCl3, 300 MHz): δ 8.91 (s, Ar-1), 8.28 (dd, J = 8.7 Hz,

Ar-2), 7.78 (d, J = 4.2 Hz, Ar-H), 7.55 (m, Ar-H), 7.33 (at,

Ar-H), 4.38 (t, 2H, J = 7.2 Hz, H-a), 1.91 (m, 2H, H-b), 1.42

(m, 2H, H-c), 0.98 (t, 3H, J = 7.2 Hz, H-d); 13C NMR (CDCl3,

75 MHz): δ 145.6, 143.2, 136.5, 134.1, 133.7, 131.4, 130.5,

130.3, 127.5, 126.2, 123.2, 123.0, 122.6, 109.1, 32.7, 29.1, 27.3,

22.4, 14.8; Elemental analysis: Calcd C: 71.5%, H: 4.6%, N:

6.1%; found C: 69.3%, H: 4.3%, N: 6.0%.

Poly{[N-octylcarbazole-3,6-diyl][4-phenylpyridine-2,6-diyl]} (P2a)Yellow powder; yield: 39%; IR (KBr, υ/cm−1): 3060, 2950,

2862, 1651, 1590, 1326, 1145; 1H NMR (CDCl3, 300 MHz):

δ 8.94 (s, Ar-1), 8.54–7.47 (m, Ar Hs), 4.38 (t, 2H, H-a), 1.93

(m, 2H, H-b), 1.27 (m, 10H, H-c,d,e,f,g), 0.88 (t, 3H, H-h);13C NMR (CDCl3, 75 MHz): δ 150.6, 148.3, 147.1, 144.4,

139.8, 136.5, 129.0, 127.3, 126.2, 120.7, 118.1, 116.5, 110.5,

35.2, 30.1, 29.2, 28.7, 27.2, 21.9, 14.8; Elemental analysis:

Calcd C: 86.5%, H: 6.9%, N: 6.5%; found C: 83.3%, H: 6.7%,

N: 6.1%.

Poly{[N-octylcarbazole-3,6-diyl][4-(3-nitrophenyl)-pyridine-2,6-diyl]} (P2b)Yellow powder; yield: 46%; IR (KBr, υ/cm−1): 3070, 2950,

2840, 1654, 1586, 1345, 1145, 802; 1H NMR (CDCl3, 300

MHz): δ 8.96 (s, Ar-8), 8.58 (s, Ar-7), 8.33–8.22 (m, Ar-H), 8.0

(d, J = 7.8 Hz, Ar-H), 7.92 (s, Ar-H), 7.66 (at, Ar-H), 7.5 (d, J =

8.7 Hz, Ar-H), 4.4 (t, 2H, J = 6.9 Hz, H-a), 1.93 (m, 12H,

H-b,c,d,e,f,g), 0.86 (t, 3H, J = 6.9 Hz, H-h); 13C NMR (CDCl3,

75 MHz): δ 148.7, 144.1, 141.0, 136.9, 134.3, 130.1, 130.0,

127.6, 124.6, 124.5, 123.1, 122.4, 109.5, 31.7, 29.3, 29.1, 28.4,

27.2, 22.6, 14.0; Elemental analysis: Calcd C: 78.3%, H: 6.1%,

N: 8.8%; found C: 77.1%, H: 5.9%, N: 8.2%.

Poly{[N-octylcarbazole-3,6-diyl][4-(3-hydroxy-phenyl)pyridine-2,6-diyl]} (P2c)Brownish-black solid; yield: 42%; IR (KBr, υ/cm−1): 3345,

3085, 2925, 2840, 1640, 1589, 1350, 1152; 1H NMR (CDCl3,

300 MHz): δ 8.94 (s, Ar-H), 8.89 (m, Ar-H), 8.84–8.81 (m,

Ar-H), 8.22–8.17 (m, Ar-H), 7.49–7.46 (m, Ar-H), 5.31 (s,

OH), 4.36 (t, 2H, J = 7.1 Hz, H-a), 2.20 (m, 2H, H-b),

1.45–1.34 (m, 10H, H-c,d,e,f,g), 0.87 (t, 3H, J = 7.2 Hz, H-h);13C NMR (CDCl3, 75 MHz): δ 153.1, 145.2, 144.3, 141.1,

139.0, 137.2, 134.4, 132.1, 129.3, 127.2, 125.3, 122.6, 120.2,

117.3, 108.2, 39.2, 29.4, 28.6, 28.2, 26.3, 22.5, 15.1; Elemental

analysis: Calcd C: 83.4%, H: 6.7%, N: 6.2%; found C: 82.1%,

H: 6.4%, N: 6.0%.

Poly{[N-octylcarbazole-3,6-diyl][4-(3-bromophenyl)-pyridine-2,6-diyl]} (P2d)Dark yellow precipitates; yield: 40%; Rf: 0.47; IR (KBr,

υ/cm−1): 3020, 2960, 2855, 1651, 1587, 1343, 1144, 668;1H NMR (CDCl3, 300 MHz): δ 8.92 (s, Ar-1), 8.28 (d, J =

7.5 Hz, Ar-H), 7.92–7.88 (m, Ar-H), 7.63–7.49 (m, Ar-H), 7.33

(at, Ar-H), 4.37 (t, 2H, J = 6.6 Hz, H-a), 1.92 (m, 2H, H-b),

1.36–1.26 (m, 10H, H-c,d,e,f,g), 0.87 (t, 3H, J = 6.9 Hz, H-h);13C NMR (CDCl3, 75 MHz): δ 144.0, 142.2, 137.2, 133.1,

130.8, 130.4, 130.4, 130.3, 127.5, 127.3, 123.2, 123.1, 123.0,

122.2, 109.3, 31.7, 29.3, 29.1, 28.9, 27.3, 22.6, 14.1; Elemental

analysis: Calcd C: 73%, H: 5.6%, N: 5.5%; found C: 70%, H:

5.4%, N: 5.2%.

AcknowledgementsThe authors gratefully acknowledge a research grant from

Quaid-i-Azam University, Islamabad, under the URF program.

M. I. gratefully acknowledges a research scholarship from

HEC, Islamabad, under the HEC Indigenous PhD Scholarship

5000 Scheme.

Beilstein J. Org. Chem. 2011, 7, 638–647.

647

References1. Burroughes, J. H.; Bradley, D. D. C.; Brown, A. R.; Marks, R. N.;

Mackay, K.; Friend, R. H.; Burns, P. L.; Holmes, A. B. Nature 1990,347, 539. doi:10.1038/347539a0

2. Morin, J. F.; Beaupré, S.; Leclerc, M.; Lévesque, I.; D’Iorio, M.Appl. Phys. Lett. 2002, 80, 341. doi:10.1063/1.1433917

3. Grimsdale, A. C.; Chan, K. L.; Martin, R. E.; Jokisz, P. G.;Holmes, A. B. Chem. Rev. 2009, 109, 897. doi:10.1021/cr000013v

4. Winder, C.; Sariciftci, N. S. J. Mater. Chem. 2004, 14, 1077.doi:10.1039/b306630d

5. Frampton, M. J.; Namdas, E. B.; Lo, S. C.; Burn, P. L.; Samuel, I. D. W.J. Mater. Chem. 2004, 14, 2881. doi:10.1039/b400160e

6. Zhang, X.; Yang, C.; Chen, L.; Zhang, K.; Qin, J. Chem. Lett. 2006, 35,72. doi:10.1246/cl.2006.72

7. Forrest, S. R. Org. Electron. 2003, 4, 45.doi:10.1016/j.orgel.2003.08.014

8. Grigalevicius, S.; Simokaitiene, J.; Grazulevicius, J. V.; Ma, L.; Xie, Z.Synth. Met. 2008, 158, 739. doi:10.1016/j.synthmet.2008.04.025

9. Grigalevicius, S.; Ledeikis, E.; Grazulevicius, J. V.; Gaidelis, V.;Antulis, J.; Jankauskas, V.; Van, F. T.; Chevrot, C. Polymer 2002, 43,5693. doi:10.1016/S0032-3861(02)00466-4

10. Xia, C.; Advincula, R. C. Macromolecules 2001, 34, 5854.doi:10.1021/ma002036h

11. Li, H.; Zhang, Y.; Hu, Y.; Ma, D.; Wang, L.; Jing, X.; Wang, F.Macromol. Chem. Phys. 2004, 205, 247. doi:10.1002/macp.200300037

12. Chen, J. P.; Natansohn, A. Macromolecules 1999, 32, 3171.doi:10.1021/ma981609b

13. Huang, J.; Niu, Y.; Yang, W.; Mo, Y.; Yuan, M.; Cao, Y.Macromolecules 2002, 35, 6080. doi:10.1021/ma0255130

14. Grigoras, M.; Antonoaia, N. C. Eur. Polym. J. 2005, 41, 1079.doi:10.1016/j.eurpolymj.2004.11.019

15. Liou, G. S.; Hsiao, H. S.; Chen, H. W. J. Mater. Chem. 2006, 16, 1831.doi:10.1039/b602133f

16. Fu, H. Y.; Wu, H. R.; Hou, X. Y.; Xiao, F.; Shao, B. X. Synth. Met.2006, 156, 809. doi:10.1016/j.synthmet.2006.04.013

17. Leclerc, M.; Michaud, A.; Blouin, N. Adv. Mater. 2007, 19, 2295.doi:10.1002/adma.200602496

18. Zou, Y.; Gendron, D.; Aich, R. B.; Najari, A.; Leclerc, M.Macromolecules 2009, 42, 2891. doi:10.1021/ma900364c

19. Aïch, R. B.; Blouin, N.; Bouchard, A.; Leclerc, M. Chem. Mater. 2009,21, 751. doi:10.1021/cm8031175

20. Pan, X.; Liu, S.; Chan, H. S. O.; Ng, S. C. Macromolecules 2005, 38,7629. doi:10.1021/ma050425b

21. Zheng, J.; Zhan, C.; Qin, J.; Zhan, R. Chem. Lett. 2002, 1222.doi:10.1246/cl.2002.1222

22. Jenekhe, S. A.; Lu, L.; Alam, M. M. Macromolecules 2001, 34, 7315.doi:10.1021/ma0100448

23. Beginn, C.; Gražulevičius, J. V.; Strohriegl, P.; Simmerer, J.; Haarer, D.Macromol. Chem. Phys. 1994, 195, 2353.doi:10.1002/macp.1994.021950706

24. He, Y.; Zhong, C.; He, A.; Zhou, Y.; Zhang, H. Mater. Chem. Phys.2009, 114, 261. doi:10.1016/j.matchemphys.2008.09.020

25. Liu, Y.; Di, C.-a.; Xin, Y.; Yu, G.; Liu, Y.; He, Q.; Bai, F.; Xu, S.; Cao, S.Synth. Met. 2006, 156, 824. doi:10.1016/j.synthmet.2006.04.011

26. Zimmermann, E. K.; Stille, J. K. Macromolecules 1985, 18, 321.doi:10.1021/ma00145a003

27. Liaw, D.-J.; Wang, K.-L.; Chang, F.-C. Macromolecules 2007, 40,3568. doi:10.1021/ma062546x

28. Zheng, J. Y.; Feng, X. M.; Bai, W. B.; Qin, J. G.; Zhan, C. M.Eur. Polym. J. 2005, 41, 2770. doi:10.1016/j.eurpolymj.2005.05.020

29. De Rossi, U.; Moll, J.; Kriwanek, J.; Daehne, S. J. Fluoresc. 1994, 4,53. doi:10.1007/BF01876654

30. Koch, W.; Heitz, W. Makromol. Chem. 1983, 184, 779.doi:10.1002/macp.1983.021840412

31. Liu, S.; Jiang, P.; Song, G.; Liu, R.; Zhu, H. Dyes Pigm. 2009, 81, 218.doi:10.1016/j.dyepig.2008.10.010

License and TermsThis is an Open Access article under the terms of the

Creative Commons Attribution License

(http://creativecommons.org/licenses/by/2.0), which

permits unrestricted use, distribution, and reproduction in

any medium, provided the original work is properly cited.

The license is subject to the Beilstein Journal of Organic

Chemistry terms and conditions:

(http://www.beilstein-journals.org/bjoc)

The definitive version of this article is the electronic one

which can be found at:

doi:10.3762/bjoc.7.75